Ventilation, smoking and exerciseIB MYP Sciences: Revision notes

Ventilation is the movement of air into and out of the lungs. It works because changing the volume of the chest changes the pressure inside it. Air always flows from a region of higher pressure to a region of lower pressure.

Inhalation (breathing in)

• The intercostal muscles contract, moving the ribs up and out
• The diaphragm contracts and flattens, moving down
• The volume of the chest increases
• The pressure inside falls below atmospheric pressure, so air flows in

Exhalation (breathing out)

• The intercostal muscles and diaphragm relax; the ribs move down and in, and the diaphragm moves up into a dome
• The volume of the chest decreases
• The pressure rises above atmospheric pressure, so air is forced out

Exhaled air is different from inhaled air because of gas exchange in the lungs and respiration in the body.

• Oxygen: about 21% in inhaled air and about 16% in exhaled air. Some is absorbed into the blood for respiration.
• Carbon dioxide: about 0.04% in inhaled air and about 4% in exhaled air. It is made in respiration, carried by the blood and diffuses into the alveoli.
• Water vapour: more in exhaled air. Water evaporates from the moist lining of the lungs and is also made in respiration.

Exhaled air is still about 16% oxygen, which is why mouth-to-mouth resuscitation can work.

Breathing rate is the number of breaths per minute. At rest it is about 12 to 20 breaths per minute.

During exercise the muscles respire faster. They need more oxygen and make more carbon dioxide. The breathing rate and the depth of each breath increase to take in more oxygen and remove more carbon dioxide.

After exercise the rate stays high for a short time, then returns to normal. A fitter person usually recovers more quickly.

Tobacco smoke harms the body in several ways:

• Tar: a sticky black substance that coats the airways and damages the cilia (tiny hairs that sweep mucus out). It also contains chemicals that cause cancer.
• Nicotine: an addictive drug that makes it hard to quit. It increases heart rate and blood pressure.
• Carbon monoxide: a poisonous gas that combines with haemoglobin in red blood cells, so the blood carries less oxygen.

Breathing in other people's smoke (second-hand smoke) is also harmful.

• Bronchitis: the airways become inflamed and filled with mucus because the cilia are damaged. Symptoms are a persistent cough and breathlessness.
• Emphysema: the walls of the alveoli break down, so the surface area for gas exchange falls. The person is short of breath and cannot get enough oxygen.
• Lung cancer: chemicals in tar make cells divide in an uncontrolled way, forming a tumour.

These diseases can be fatal. Stopping smoking reduces the risk.

Criterion D questions ask you to weigh up the social, economic and ethical effects of an issue.

• Social: health of smokers and non-smokers, family impact, second-hand smoke
• Economic: cost of healthcare, tobacco tax income, businesses affected, cost of cigarettes to families
• Ethical: personal freedom against protecting other people's health

A strong answer gives points on both sides, then a justified conclusion. Laws such as smoking bans, higher tobacco taxes and plain packaging are examples to discuss.